1. Field of Invention
Embodiments of the invention relate generally to electronic devices and, more specifically, in certain embodiments, to methods of forming connections to data cells.
2. Description of Related Art
Many types of electronic devices have data cells. Typically, the data cells each include a data element (e.g., a memory element, an imaging element, or other device configured to output data, such as various kinds of sensors) and, in some instances, an access device, such as a transistor or diode. Generally, the access device controls access to the data element, and the data element outputs signals indicative of stored or sensed data.
Often the data elements are arranged in an array, e.g., generally in rows and columns. Data cells within the array are accessed, e.g., written to or read from, through circuitry near the periphery of the array. For instance, sense amplifiers or other sensing circuitry are often positioned adjacent arrays of data cells for reading data. Similarly, address decoders, e.g., row and column address decoders, are often disposed adjacent the array for addressing particular data cells or groups of data cells.
Devices in the array often are structured differently from structures in the periphery. Array transistors may be formed from materials that are different from the materials used to form transistors in the periphery, and the dimensions, e.g., thickness, of materials in these devices may be different. In some devices, differences between the array and periphery are accommodated with multiple lithography steps. For instance, a first photolithography tool may pattern a first material in the array, and a second, different photolithography tool, may pattern a second, different material in the periphery. In this way, different design tradeoffs, e.g., size versus signal quality, may be made between the array devices and the periphery devices.
These differences, however, can increase the cost of electronic devices. Each lithography step adds costs, and certain lithography steps are particularly expensive. Typically, manufacturing lines use several different generations of lithography equipment, ranging from more advanced, newer equipment to less capable, older equipment. The newer equipment is typically much more expensive, so designers strive to reduce the number of manufacturing steps that use the newer lithography equipment. Patterning array and periphery devices, however, is often done with separate lithography steps on the newer equipment, adding to the cost of electronic devices.